(a) Field of the Invention
The present invention is directed to a method for removing resin clogged in a nozzle of a motor-driven injection molding machine by moving forward a screw of the machine. More particularly, the present invention is directed to a method of this kind adapted to protect a servomotor for driving the screw from being overloaded.
(b) Description of the Related Art
While an injection molding machine is operated, there are occasions when molten resin is cooled and solidified in a nozzle and finally clogs the nozzle. This prevents continuation of injection molding cycles. Particularly in the case where retracting of the nozzle, or a so-called sprue break, is not performed in each injection molding cycle to set the nozzle apart from the mold. The nozzle is readily cooled by the mold contacting the nozzle, resulting in solidification of molten resin at the distal end of the nozzle and hence clogging of the same.
Measures conventionally taken to remove the solidified resin when the nozzle becomes clogged are to disassemble the nozzle, or move the screw forward through manual operation of an injection mechanism to discharge the solidified resin by applying a high pressure thereto.
If the latter-mentioned method for removing the resin in the clogged nozzle is applied to a hydraulic injection molding machine, no particular problems will arise. However, if this method is used with an injection molding machine using a motor, e.g., a servomotor, as the driving power source of the injection mechanism, an excessive load may be placed on the motor when the resin clogged in the nozzle is discharged. On such occasions, a large current flow occurs in the motor for a long period of time. Thus, the motor and the components of an electronic circuit for driving the motor, e.g., power transistors, will have shortened lives or be destroyed.